1. Field of the Invention
The present invention concerns a freezer unit (including air conditioner) composed by providing a plurality of compressors for compressing refrigerant in parallel.
2. Detailed Description of the Prior Art
In general, the lubricant oil (called simply oil, hereinafter) that the compressor holds is discharged from the compressor with compressed refrigerant, lowering the oil level in the compressor and the lubrication becomes insufficient; therefore, an oil separator is installed in the refrigerant discharge pipe, in a way to return oil separated from refrigerant by this oil separator.
On the other hand, in a freezer unit connecting in parallel a plurality of compressors provided with a oil reservoir section in the low pressure portion, oil quantity balance is maintained by communication respective oil reservoir sections through an oil balance pipe.
However, in case of freezer unit wherein oil quantity balance is maintained by communication respective oil reservoir sections through an oil balance pipe, when at least one of compressors is a capacity controllable compressor, or, when a plurality of compressors of different compression capacity are connected in parallel for enlarging the scale, oil increases in the high output compressor, oil lacks in the low output compressor, abrasion progresses at the sliding parts of oil lacking compressors, and the apparatus life reduces or other problems occur, because the pressure difference is generated in the compression vessel, oil is sucked by the high output compressor, or for other reasons.
It is necessary to connect an oil balance pipe having a large diameter to a compressor of high output, in order to solve the imbalance of oil quantity; however, the oil balance pipe becomes complicated, and increases the cost, because an effort is applied to the oil balance pipe when the compressor is started.
Also, in a freezer unit comprising a plurality of compressors of a vessel structure having a low pressure portion and a high pressure portion divided through a discharge port of a compression pump and internal high pressure compressors are installed in parallel, an oil sensor for detecting the oil level surface is installed in respective compressors, and the oil quantity balance of respective compressors is maintained by controlling the oil return quantity from the oil separator based on the state of the oil level surface.
However, the oil sensor is complicated in structure and expensive. In, addition, the oil return control circuit also become complicated and expensive.
[Means for solving the problems]
Therefore, it is necessary to avoid lack of oil in some compressors by a simple composition without cost increase, even if refrigerant compression capacity differs or the passage resistance of the refrigerant discharge pipe differs from one compressor to the other, and it has been the problem to be resolved.
The present invention intends to solve the problems of the prior art mentioned above, by providing:
a freezer unit of a first composition comprising a single refrigerant circuit where a plurality of internal high pressure type compressors are installed in parallel, wherein an oil separator is installed in a discharged refrigerant junction pipe where refrigerants discharged from respective compressors meet, a first kind of oil return pipe leading to a refrigerant suction pipe of a first compressor from this oil separator is installed, and a second kind of oil return pipe leading to a refrigerant suction pipe of a second compressor from the regular oil level height of the first compressor,
a freezer unit of a second composition comprising a refrigerant circuit where a plurality of internal high pressure type compressors is installed in parallel, wherein an oil separator is installed in a discharged refrigerant junction pipe where refrigerants discharged from respective compressors meet, a first kind of oil return pipe provided with an on-off valve in the pipe leading to a refrigerant suction pipe of each compressors from this oil separator is installed, and a second kind of oil return pipe leading to a refrigerant suction pipe of a second compressor from the regular oil level height of the first compressor is installed,
a freezer unit of a third composition, wherein the first compressor is a variable compression capacity type compressor in the freezer unit of said first or second composition,
a freezer unit of a fourth composition comprising a refrigerant circuit where a plurality of compressors of a vessel structure having a low pressure portion and a high pressure portion divided through a discharge port of a compression pump are installed in parallel, wherein an oil balance pipe provided with a pressure reduction means leading from the high pressure portion of a compressor to a refrigerant suction pipe of another compressor is installed,
a freezer unit of a fifth composition comprising a refrigerant circuit where a first compressor of a vessel structure having a low pressure portion and a high pressure portion divided through a discharge port of a compression pump and a second compressor of a high pressure vessel structure are installed in parallel, wherein an oil balance pipe provided with a pressure reduction means leading to a refrigerant suction pipe of the second compressor from the high pressure portion of the second compressor, and an oil balance pipe provided with a pressure reduction means leading to a refrigerant suction pipe of the first compressor from the vicinity of the regular oil level surface of the second compressor is installed,
a freezer unit of a sixth composition, wherein one end of the oil balance pipe is connected to the ascending slope portion of a branched refrigerant suction pipe in the freezer unit of said fourth or fifth composition, and
a freezer unit of a seventh composition, wherein the refrigerant suction pipe is connected horizontally to the compressor, and one end of the oil balance pipe is connected to a position where a central angle xcex8 on an arc between the refrigerant suction pipe and the oil balance pipe becomes equal or inferior to 45 degrees, at the underside of this refrigerant suction pipe connection part in the freezer unit,